A diesel engine (DE) is one of the most efficient internal combustion engines, as it is reduced in the discharge of carbon dioxide (CO2) per certain output and economical so as to be able to use a low-quality fuel such as heavy oil. There is a tendency that the diesel engines are frequently used to prevent global warming. This is because it is reconsidered that cars and a stationary generator using a diesel engine have high-energy efficiency with small amount of discharge of carbon dioxide (CO2).
However, a lot of particulate matter (PM) in which unburned hydrocarbons are united with soot is discharged from these diesel engines using heavy oil or light gas oil as its fuel to be the main cause behind the pollution and a social problem. Various industries such as diesel engine makers and car makers undergo researches into and developments in the removal of PM and have made studies and inventions concerning filters having excellent ability of removing PM, prefilter oxidation catalysts and DP (Diesel Particulate) filters (DPF) so devised that the filter is made to carry an oxidation catalyst to oxidize nitrogen monoxide (NO) in exhaust gas into nitrogen dioxide (NO2) to burn soot, in order to prevent or retard clogging with soot for a long period of time (Non-Patent Document 1, for example).
Many of these technologies intend to filter exhaust gas by passing it through a thin wall which is porous ceramics several μm in size. Plate or cylindrical filters obtained by calcining metals or ceramics, filters using a honeycomb ceramic porous molded body of which the meshes are alternately filled up and filters using fine metal wire woven fabrics are known. Also, filters obtained by providing these filters with the ability of oxidizing NO into NO2 to oxidize and burn soot with the intention of preventing or limiting clogging of these filters (Patent Documents 1 and 2 and Non-Patent Document 2, for example).
Non-Patent Document 1: Japan Environmental Management Association for Industry, Environmental Management Vol. 37, p 441-449
Patent Document 1: Publication of Japanese Patent Application Laid-Open No. 1-318715
Patent Document 2: Publication of Japanese Patent Application Laid-Open No. 60-235620
Non-Patent Document 2: Society of Automotive Engineers of Japan Academic Lecture Publisher No. 22-2